Pythagoras considered the number 1 to be the generator of all other numbers.   It was used to characterize reason.

The number 2 was the first female number.   It was the number of opinion and division.

The Chinese yin and yang express the same sentiments: Yin represents the feminine and negative principle, like passivity and darkness.   The yang represents the bright and masculine principle.

Pythagoras viewed the number 3 as masculine.   It has a beginning, a middle, and an end.

4 was the number of justice and order.

5 represents the union of the first female number 2 and the first male number 3,
    and as such it was the number of love and marriage.

6 is the first perfect number: 6 = 1 + 2 + 3
6 is the product of the first female number (2) and the first male number (3).

10 was the most revered number because it represented the cosmos as a whole.   (1 + 2 + 3 + 4 = 10)
10 combined all the properties of
        uniqueness (expressed by 1)
        polarity (expressed by 2)
        harmony (expressed by 3) and
        space and matter (expressed by 4)